NewWorld Macs are signficantly changed from their predecessors (referred to as OldWorld Macs, although not officially called that). Strangely enough, the easiest way to tell if a Mac NewWorld or OldWorld is just look at the "happy Mac" icon that appears as soon as you power on the machine. OldWorld Macs have a monochrome happy Mac icon, NewWorld Macs have a colorized happy Mac icon. NewWorld Macs also have radically changed ROM formats (hence the lack of support for older Mac OS versions). This is not a problem with Mac OS, but it caused quite a stir among the PowerPC Linux community, in how to support both methods of booting (although, they did it).

The "NewWorld" name likely derives from the enum listing in Apple's header files for gestalt code 406 (which all NewWorld Macs return for the 'mach' selector) "NewWorldMac". There is no such official moniker for OldWorld macs, since they all returned a different 'mach' result depending on which type of machine they are. NewWorld macs are better idenitfied with the 'cput' and 'pclk' selectors. (see node at gestalt for more on the gestalt selectors in Mac OS)